This invention relates to a metal gasket to be interposed between a cylinder block and a cylinder head of an internal combustion engine.
Such a metal gasket is known as shown in FIGS. 1 to 3 illustrating a conventional metal gasket 3 as an example. As shown in partial sectional views, FIGS. 2 and 3, the metal gasket 3 includes a metal functional layer 1 made of a stainless steel or the like and a backup metal plate 2 made of a stainless steel or the like. The backup metal plate 2 is laminated on the metal functional layer and folded over the metal functional layer.
The metal gasket 3 is generally formed with cylinder openings 4, coolant openings 5, lubricant openings 6 and bolt holes 7.
The metal functional layer 1 has a embossment 8 formed along the peripheral edge of each of the cylinder openings 4 and a fold-over tab 9 is formed by folding the inner periphery of the cylinder opening 4 of the backup metal plate 2 over the peripheral edge of the cylinder opening 4 of the metal functional layer 1 to fasten the peripheral edge therebetween. Thus, the foldover is made after assembling the metal functional layer 1 and the backup metal plate 2 as shown in FIGS. 2 and 3. FIGS. 2 and 3 illustrate sections of the metal gasket 3 taken along lines II--II and III--III in FIG. 1 on an enlarged scale, respectively.
In a metal gasket to be interposed between a cylinder block and a cylinder head of an internal combustion engine, sealing at peripheral edges of cylinder openings 4 is particularly important. Therefore, the metal gasket 3 shown in FIG. 1 includes annular embossments 8 formed at the peripheral edges of the cylinder openings 4 and the fold-over tabs 9 formed by folding the inner peripheries of the openings 4 of the backup metal plate 2 for ensuring the sealing about the cylinder openings 4.
In this case, the seal is enhanced by the elasticity of raised portions of the embossments 8 and by increased thicknesses of the fold-over tabs 9 causing clamping pressure to increase. However, since the fold-over tabs 9 are formed by plastic deformation of the metal plate, there is a tendency of the fold-over tabs to be uneven in thickness and at the same time there is a risk of cracks occurring in the fold-over tabs. Therefore, it is difficult to exactly control surface pressure distribution only by the fold-over tabs.